Comprehensive yet quick video overview that explains how you can safely and non-destructively convert a Windows 10 machine from legacy BIOS to UEFI disk partitioning; and how you can automate the conversion as part of your in-place upgrade process from Windows 7 to Windows 10.

One thing I noticed when performing the conversion during an upgrade task sequence, you will lose the ability to "rollback" to previous build of Windows 10. This makes sense but I didn't see it documented anywhere.

It's necessary to have Creators Update if you wish to run the tool from within Windows (Full OS). MBR2GPT does support older versions of Windows 10 when ran from the WinPE thats included in Windows ADK 1703.

Sorry - typo on my part. 0x571 is what I meant to type. What make/model is the system and how was it built? If I had to guess, it is having an issue with the third partition. Type 39 is Bell Labs partition type.

I understand that the MBR2GRT.exe will support versions of Win 10 previous to 1703 and should work when booted from a Win PE 1703 disk.

So I downloaded & install Windows ADK 1703 & made a Win PE disk. I booted from that disk and ran MBR2GPT /validate and the result was "unable to validate disk." Any ideas? It's a 500gb disk with about 90gb free. Is free space the problem?

But, again a shoutout to Microsoft developers: The errors you (Developers) throw are not there for so only you can debug your code. They are first and foremost for the user to understand what has gone wrong. So the question remains: Why is there no error message on validation that states: There are too many partition on disk x, please reduce the number of partitions to at most 3 to be able to convert. --> This should not be that hard.

MBR works with disks up to 2 TB in size, but it can’t handle disks with more than 2 TB of space. MBR also only supports up to four primary partitions — if you want more, you have to make one of your primary partitions an “extended partition” and create logical partitions inside it. This is a silly little hack and shouldn’t be necessary.GPT stands for GUID Partition Table. It’s a new standard that’s gradually replacing MBR. It’s associated with UEFI — UEFI replaces the clunky old BIOS with something more modern, and GPT replaces the clunky old MBR partitioning system with something more modern. It’s called GUID Partition Table because every partition on your drive has a “globally unique identifier,” or GUID — a random string so long that every GPT partition on earth likely has its own unique identifier.

This system doesn’t have MBR’s limits. Drives can be much, much larger and size limits will depend on the operating system and its file systems. GPT allows for a nearly unlimited amount of partitions, and the limit here will be your operating system — Windows allows up to 128 partitions on a GPT drive, and you don’t have to create an extended partition.

On an MBR disk, the partitioning and boot data is stored in one place. If this data is overwritten or corrupted, you’re in trouble. In contrast, GPT stores multiple copies of this data across the disk, so it’s much more robust and can recover if the data is corrupted. GPT also stores cyclic redundancy check (CRC) values to check that its data is intact — if the data is corrupted, GPT can notice the problem and attempt to recover the damaged data from another location on the disk. MBR had no way of knowing if its data was corrupted — you’d only see there was a problem when the boot process failed or your drive’s partitions vanished.

Just done this on one of our work machines. If this works it'll save us bloody hours so cheers MS. One question though it seems to have gotten to "Fixing drive letter mapping" and stopped. Checking everything else it seems fine, disk converted , lovely... so is it safe to restart and change the BIOS/UEFI options or does this take a dam sight longer than the video hinted at?Up to 40 minutes now.

basically you must not have more than three partitions and not any free space left on the hard drive.if you check the list of partition on DISKPART you will see that even the free space is listed as a partition.you can use tools like disk manager (built-in windows) or minitool to resize the current partitions to take up the left over free space then validate mbr2gpt again.

I noticed that when I try to shrink Volume via Disk management it just hangs on the next window, the Activity Monitor shows a Service Host: Disk Defragmenter / Optimize drives process tat is using 10% CPU, has a growing memory usage as well as about 10MB/s disk usage

The exact same thing happens when the MBR2GPT process is "stuck" on Trying to shrink the OS partitionI partitioned the disk using a 3rd party software and create a 2GB Unallocated sector and tried again, same issue.

I also remove the 2 recovery partition on the drive. (I have a USB disk with the windows recovery system)I am not sure what is going on, but I would really hate to do a complete wipe of the drive and start from scratch.

Do you have the same problem when running MBR2GPT from WinPE? Chances are, you have something running in the full OS that is causing the issue and this is why it is recommended to run MBR2GPT in WinPE.

But, before the last time I tried it, when it worked, I used the Defragmenter tool to "optimize" my SSD, then it did the same thing, but now it worked. I can post the logs if it is going to help anyone.

I did have a boot problem, my BCD was effed up.

For this I did you WinPE and had to do the assign a letter to the EFI partition, then do the bcdboot c:\windows /s e: command to get the BCD stuff from the installed windows to the EFI partition, now it boots and switched the GPT so all is well.

I Had the same error while trying to convert my mbr hard disk to gpt.what I did for getting success was the following:1.- checking my partitions in computer management, I saw my two partitions (system reserved and OS ) were primary partitions, but data partition Or D: (as I use to call it) was in logical partition state.2.- I installed Minitool Partition Wizard and converted logical partition to primary.3.- Run into windows Enviroment the mbr2gpt /convert /disk:"number of the disk" /allowFullOS and the... IT WORKED!

I Had the same error while trying to convert my mbr hard disk to gpt.what I did for getting success was the following:1.- checking my partitions in computer management, I saw my two partitions (system reserved and OS ) were primary partitions, but data partition Or D: (as I use to call it) was in logical partition state.2.- I installed Minitool Partition Wizard and converted logical partition to primary.3.- Run into windows Enviroment the mbr2gpt /convert /disk:"number of the disk" /allowFullOS and the... IT WORKED!